Wind axis and cross-wind axis turbines are the predominant wind turbines presently in use and under study. A wind axis turbine includes a number of blades mounted for rotation about a central horizontal column having an axis of rotation that must be closely aligned with the wind to produce power efficiently. Since wind direction tends to vary over time at most sites, high efficiency can be achieved only if the horizontal axis can be rotated to provide the close alignment. However, structure for rotating the horizontal axis into the wind tends to be expensive, resulting in poor power-cost ratios for very high power wind turbines.
Wind driven vertical turbines typically include an assembly of airfoils or blades mounted for wind-driven structure. Vertical wind driven turbines respond to wind from any direction without shift of the column or base structure thereof. However, to improve blade efficiency, by obtaining a more favorable blade angle of attack to the wind, it is often necessary to rotate each blade about an individual axis thereof as the assembly rotates about the vertical column. Known structures such as a type disclosed in U.S. Pat. No. 4,049,362 to Rineer, a ring gear arrangement as disclosed in U.S. Pat. No. 3,903,072 to Quinn, or a circular track and bearing arrangement as disclosed in German Pat. No. 742,788 to Hartwagner. The blade angle of attack control structures disclosed in the aforesaid patents also vary the blade angle of attack in response to changes in wind speed or velocity.
The foregoing blade control arrangements have a number of disadvantages, one being that a higher than average on site wind velocity is often necessary to overcome inertia of the ring gear, gear train or circular track mechanisms to initiate turning of the blades. Also, to maintain blade rotation, a certain amount of wind power is necessary to overcome inertia of the ring gear, gear train or circular track mechanisms to initiate turning of the blades. Also, to maintain blade rotation, a certain amount of wind power is necessary to overcome friction generated by these blade control mechanisms, adversely affecting power/cost ratios. Further, since gears employed in these prior art mechanisms rotate constantly, in wearing contact with each other, and operate under variable wind velocity conditions, frequent maintenance and/or replacement may be necessary, particularly after periods of excessive wind velocities. To generate sufficient wind power to achieve economical operation, vertical wind turbines generally include large airfoils. Devices to control such airfoils can be very costly.
Another problem associated with certain known relatively high efficiency cross-wind axis wind turbines is that the blades have complex shapes, thus being expensive to manufacture. Other turbines of this type are inefficient because the blades are not designed so they are always oriented to the wind for optimal wind energy absorption.
It is accordingly an object of the invention to provide a vertical wind turbine having a low inertia blade control mechanism for controlling both the speed and orientation of plural vertical blades under variable wind conditions to maximize conversion of wind power to usable power.
Another object of the invention is to provide a wind turbine having a blade control mechanism that is economical in design and capable of reliable operation in rugged and hostile environments, as occurs in on-site wind locations.
Yet another object is to provide for controlled orientation of blades in the vertical wind turbine of the invention to regulate angular velocity of the blades and hence conversion efficiency of the turbine.
Still a further object is to provide a wind turbine that is simple, reliable and inexpensive to construct.